The actor tweeted: "If Wales wins she better say yes ... Go Wales!!!" Roberts, 32, said she and The Hoff were planning to watch the final broadcast at Millennium Stadium next week if Wales won.
He has been dating Roberts, a former department store worker, for seven months.
Meanwhile, Barrie-John Partridge went to support Wales with his father last night - and left a little bit of his dad behind.
It was the latest effort in his pre-game ritual after his dad died from cardiac problems in August.
The ritual began with taking the ashes to every Wales game. Then, Partridge sprinkled some on the pitch in Wellington following Wales' quarter-final victory over Ireland.
"Most people who found out are pretty okay with it," Partridge said.
"There have been a couple of interesting looks.
"Mum was thinking it was a bit weird at the start. We talked about it and she realised it's what Dad was all about. It's what he would have wanted."
He said it was an unusual item to take into the ground but had not been questioned by security yet.
But Rugby 2011 spokesman Mike Jaspers said no one would be allowed to tip ashes on to the park.
He said scattering ashes where the living play was a major cultural breach.
